Engine exhaust systems have utilized hydrocarbon retaining devices, such as hydrocarbon traps, to retain cold start emissions for later reaction, or to recirculate into the engine intake system.
However, the inventors herein have recognized that the porosity of the hydrocarbon retaining device may be too small in some examples. Specifically large molecule hydrocarbons can become irremovably lodged in the devices. On the other hand, porosity of the of the hydrocarbon retaining device may be too large in some examples where depending on the fuel combusted, a significantly large number of small molecule hydrocarbons can be produced and pass through to the exhaust.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.